Low allozyme diversity in Schwalbea americana (Scrophulariaceae), an endangered plant species

Abstract

Schwalbea americana, a hemiparasitic member of the Scrophulariaceae, is an early successional, fire-dependent species of the eastern coastal plain of North America. We sampled 13 populations across the range of this endangered perennial herb to describe allozyme diversity at 15 presumptive loci. Genetic diversity was low for the species, within populations, and for polymorphic loci (H(es) = 0.006; H(ep) = 0.005; H(T) = 0.028). Three of the 15 loci (20%) were polymorphic across the species' range, but frequencies of uncommon alleles were uniformly low (mean P = .05). No polymorphism was detected in seven populations. Population extinctions and decreases in population sizes, coupled with habitat fragmentation, may account for the low genetic diversity. The fugitive life-history characteristics of this shade-intolerant species presumably have also contributed to the loss genetics diversity by predisposing the species to founder effects and populations extinctions.